This application corresponds to Japanese Patent Application No. 2000-069990 filed in JPO on Mar. 14, 2000, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a common rail fuel injection device for injecting fuel accumulated in a pressurized state in a common rail, via injectors, and more particularly, to a common rail fuel injection device for performing fuel injection via injectors, by means of a main injection, and a pilot injection whereby a small quantity of fuel is injected prior to the main injection.
2. Description of the Related Art
In the prior art, a common rail fuel injection system is known as a method for obtaining a higher fuel injection pressure in a fuel injection system for an engine, by controlling the injection conditions of fuel from injectors, such as the injection timing and injection quantity, to optimal conditions corresponding to the operating state of the engine. A common rail fuel injection system is a system wherein an operating fluid raised to a prescribed pressure by means of a fuel supply pump, is accumulated in a pressurized state inside a common rail, and based on the action of the pressure of the operating fluid, fuel is injected from injectors disposed respectively with respect to a plurality of cylinders, into combustion chambers thereof, under optimal fuel injection conditions, such as fuel injection quantity and fuel injection time, and the like, as determined by a controller in accordance with the operating state of the engine. Each injector is provided with a control valve to perform control for passing or blocking fuel supplied via a fuel supply pipe.
If the fuel itself forms the operating fluid, then the common rail accumulates fuel in a pressurized state therein, and a fuel pressure corresponding to the injection pressure is exerted constantly in the fuel supply path formed from the common rail, via fuel supply pipes, to nozzles formed at the front end of each injector. In order that each injector injects fuel only at a prescribed time, control valves are provided which open and shut the fuel supply path by being driven by an actuator, such as an electromagnetic actuator, magnetic distortion element, or the like. The controller controls the pressure in the common rail and the operation of each injector""s control valve, in such a manner that the pressurized fuel is injected by each injector at optimal injection conditions with respect to the operating state of the engine.
In a common rail fuel injection device, the control valves are operated by actuators on the basis of electrical signals output by the controller. However, there is a delay time caused by response delay, from the time at which current is applied to the actuator due to the output signal from the controller, until the time at which the control valve actually performs an opening/shutting operation. Therefore, the target fuel injection time is determined based on the operating state of the engine, and the aforementioned response delay is taken into consideration when determining the drive time of the control valve to the injector, in other words, the output timing of the injection pulse constituting a command pulse from the controller, based on the target fuel injection time.
FIG. 5 shows an overview of a common rail fuel injection system in which a common rail fuel injection device is applied. The common rail fuel injection system 1 illustrated in FIG. 5 is a system for a six-cylinder engine, wherein fuel in a fuel tank 4 is passed through a pre-filter 5 and a filter 6 comprising a circulating valve and demoisturizer, whereupon it travels along a fuel pipe 7 and is supplied to a fuel supply pump 8, which is, for example, a variable capacity high-pressure plunger-type pump. The fuel supply pump 8 is driven by the engine output, and it raised the fuel to the prescribed pressure required, and supplies it to a common rail 2, via a fuel valve 9 and pressure control valve 11. Before the common rail 2 on the output side of the fuel supply pump 8, a pressure control valve 11 is provided in order to maintain the fuel pressure in the common rail 2 at a prescribed pressure. Fuel relieved from the fuel supply pump 8 is returned via a return pipe 12 to the fuel tank 4. The fuel inside the common rail 2 is supplied to a plurality of (six) injectors 10 (only one injector is depicted here) via a fuel supply pipe 3. Of the fuel that is supplied to the injector 10 via the fuel supply pipe 3, that fuel which is not consumed in the injection into the combustion chamber, and the fuel that is relieved by the pressure control valve 11 is returned to the fuel tank 4 by means of return pipes 13 and 14.
The controller 15 is an electronic control unit, which inputs signals from various sensors 16 in order to detect the operating state of the engine, such as, an engine cylinder discriminating sensor, a crank angle sensor for detecting the engine revolutions Ne and the top dead centre (TDC), an accelerator opening sensor for detecting the accelerator pedal operation amount Ac, a water temperature sensor for detecting the temperature of the cooling water, an inlet tube pressure sensor for detecting the internal pressure of the inlet tube, and the like. The pressure of the common rail 2 is detected by a pressure sensor 18 provided at the pressure control valve 11, and a detection signal for the fuel pressure Pr inside the common rail 2 (hereinafter, called fuel pressure in the common rail,) as detected by the pressure sensor 18 is also input to the controller 15. Based on these signals, the controller 15 controls the injection conditions for the fuel from the injectors 10, in other words, the fuel injection time (injection start timing and duration), injection quantity, and the like, in such a manner that the engine output is optimally suited to the operating state thereof. The fuel in the common rail 2 is consumed by being injected from the injectors 10, and hence the fuel pressure inside the common rail falls, but the controller 15 controls the pressure of the fuel supplied from the fuel supply pump 8 by means of the control section 19 of the pressure control valve 11, in such a manner that the fuel pressure in the common rail Pr remains uniform, or become equal to the fuel injection pressure required according to the operating state of the engine.
FIG. 6 is an approximate longitudinal diagram showing one example of an injector used in a common rail fuel injection system. The injector 10 is installed in a sealed state by means of a sealing member in a cavity portion provided in the base of the cylinder head, or the like (not illustrated). The fuel supply pipe 3 is connected to the upper side portion of the injector 10, and this fuel supply pipe 3 forms a fuel supply path in conjunction with fuel passages 21, 22 formed inside the injector 10 proper. Nozzles 25 are formed at the front end portion of the injector 10, and fuel supplied via the fuel supply path passes via a fuel reservoir 23 and needle valve 24 and is injected into the combustion chamber from the nozzles 25, which open when the needle valve 24 lifts.
In order to control the lifting of the needle valve 24, the injector 10 is provided with a needle lifting mechanism based on a pressure control chamber. An electromagnetic actuator 26 driving an electromagnetic valve is provided on the uppermost portion of the injector 10, and a control current corresponding to a command pulse from the controller 15 is supplied via a signal line 27 to the solenoid 28 of the electromagnetic actuator 26. When the solenoid 28 is excited, an armature 29 rises up and opens a control valve 32 provided at the end of the fuel path 31, thereby releasing the pressure of the fuel supplied from the fuel supply path to the pressure control chamber 30, by means of the fuel passage 31. A control piston 34 is provided in a raisable and lowerable fashion inside a cavity 33 formed inside the injector 10. Since the lifting force pushing the control piston 34 upwards due to the fuel pressure acting on the tapered face 36 surrounding the fuel reservoir 23 is greater than the force pressing down on the control piston 34 due to the lowered pressure inside the pressure control chamber 30 and the spring force of a return spring 35, the control piston 34 is raised up. Consequently, the needle valve 24 lifts and fuel is injected from the nozzles 25. The fuel injection time is determined by the lift timing of the needle valve 24, whilst the fuel injection quantity is determined by the fuel pressure in the fuel supply path, and the lifting of the needle valve 24 (amount of lift, duration of lift). In other words, the needle valve 24 is raised and lowered by the action of the fuel pressure inside the pressure control chamber 30, and the control valve 32 releases the fuel pressure inside the pressure control chamber 30 by discharging fuel from inside the pressure control chamber 30. The fuel discharged via the fuel passage 31 and the fuel which leaks into the cavity 33 and is discharged in to a low-pressure chamber 37 are returned to the fuel tank 4 by means of leak passage 38 and return pipe 13 (FIG. 3).
In general, the relationship between the fuel injection quantity at the injection 10 and the pulse width of the command pulse output by the controller 15 is determined by a map which uses the fuel pressure in the common rail Pr (fuel pressure inside the common rail 2) as a parameter. Assuming the fuel pressure in the common rail Pr is uniform, the larger the pulse width, the greater the quantity of fuel injected, whereas if the pulse width remains the same, the fuel injection quantity will rise with increase in the fuel pressure in the common rail Pr. On the other hand, the fuel injection starts and stops with a respective time delay compared to the fall time and rise time of the command pulse. Consequently, it is possible to control the injection timing and injection quantity by controlling the on timing and off timing of the command pulse. A uniform relationship between the basic injection quantity and the engine revolutions is previously determined as a basic injection quantity characteristics map, taking accelerator pedal operation amount as a parameter, and the injected fuel quantity for each fuel cycle is then determined by calculation from this basic injection quantity characteristics map, according to the current operating state of the engine.
In accordance with the fuel injection at each cylinder during the engine cycle, the fuel pressure in the common rail Pr follows a cycle whereby it starts to fall at a time delay after the start of injection, and after injection has been completed, it recovers due to output of fuel from the fuel supply pump 8 in order to inject fuel at the cylinder where next combustion is to occur according to the combustion sequence. Since the engine is a multiple-cylinder engine, as shown in FIG. 5, the controller 15 controls the fuel injection from the injector 10 separately for each cylinder.
A method for determining the output timing of the injection pulse output by the controller to the actuator of the injector in order to perform fuel injection, is disclosed, for example, in Japanese Patent Laid-open No.(Sho) 61-31643, or Japanese Patent Laid-open No.(Sho) 61-286541. Japanese Patent Laid-open No.(Sho) 61-31643 discloses a fuel injection quantity control device for an engine, wherein fuel is supplied to an engine by means of a fuel pump and the start and end of fuel injection to the engine is determined by electromagnetic injection valves, which seeks to control variation in operating characteristics caused by individual disparities or temporal change in electromagnetic injection valves by taking account of the delay time arising in the lift and fall of the needle of the electromagnetic valves, and controlling the injection start, injection end, or injection timing according to the operating characteristics of the electromagnetic injection valves, such as their fully-closed and fully-open time periods, or closing and opening speed, and the like.
Japanese Patent Laid-open No.(Sho) 61-286541 discloses a fuel injection pump provided with an electromagnetic valve between a fuel pressure chamber and a low-pressure section, the fuel injection timing and fuel injection quantity being controlled by controlling the opening and closing times of this electromagnetic valve, wherein the injection timings for all the cylinders can be controlled accurately in accordance with prescribed target values, by taking the response delay of the electromagnetic valve into account, even if only one sensor is provided for detecting the ignition timing, or the fuel injection start timing, or the like, which affect the start of fuel combustion.
As means for lowering combustion noise and preventing deterioration of exhaust gas characteristics in a diesel engine, so-called pilot injection control is performed whereby a small quantity of fuel is injected prior to the main injection. By performing this pilot injection, it is possible to raise the temperature of the combustion chamber in advance and hence prevent sudden combustion of the injected fuel, and consequently, the generation of so-called diesel xe2x80x9cknockxe2x80x9d can be prevented, and the ratio of nitrogen oxide contained in the exhaust gas can also be reduced. The pilot injection quantity is determined by taking account of the amount of nitrogen oxide generated, as determined by experimentation. Pilot injection is generally necessary when the engine is in a low-load or low-revolution operating state, and therefore the pilot injection quantity is determined either as an injection quantity of a small ratio compared to the overall injection quantity, or as a universal small absolute quantity.
In a common rail fuel injection device, the main injection time for performing the main fuel injection, the interval period from the end of the pilot injection until the main injection time, and the pilot injection quantity, are determined according to the operating state of the engine, and the output time of the pilot injection pulse output from the controller in order to perform pilot injection is calculated back from aforementioned main injection time, according to the sum of the interval period and the pilot injection period determined from the pilot injection quantity, and furthermore, the response delay from the time at which an output signal is emitted by the controller until the control valve of the injector starts to operate is also taken into account in determining the output time of the pilot injection pulse.
When performing pilot injection in a common rail fuel injection device, if injection is performed when the drive current of the injection pulse signal output from the controller is on, then when the current switches off, the rear pressure on the needle of the needle valve (pressure inside the pressure control chamber) will rise, the needle will be pushed downwards, and the nozzles are closed by the needle valve, thus ending the pilot injection. In this case, if the fuel pressure in the common rail is high, then the fuel pressure at the front end of the needle will act to push the needle upwards, and hence an additional force is required to push the needle down. If there is insufficient force pressing the needle down, then it will take time for the nozzles to close, and hence the pilot injection end time will be delayed, causing a corresponding alteration to the internal time, and in extreme cases, the pilot injection and main injection may become combined, similarly to performing main injection over a long period of time. In turn, this will cause the actual quantity of actual fuel injected to increase, leading to large torque variations and a state of over-torque, whilst also reducing the combustion noise reduction effects of the pilot injection operation.
Therefore, in a common rail fuel injection device which performs fuel injection comprising a main injection and a pilot injection implemented prior to the main injection, it is necessary to resolve the problem of ensuring a prescribed interval time, and performing accurate pilot injection to the engine by improving control of pilot injection, even in cases where the fuel pressure in the common rail increases.
It is an object of the present invention to provide a common rail fuel injection device which accumulates pressurized fuel in a common rail, and injects fuel supplied by the common rail via injectors, in a separate pilot injection and main injection, based on detection signals from detecting means for detecting the operating state of the engine, wherein the pilot injection and main injection are clearly separated, and the beneficial effects of the pilot injection in suppressing combustion noise and preventing deterioration of the exhaust gas characteristics, and the like, can be reliably obtained.
This invention relates to a common rail fuel injection device comprising: a common rail for accumulating pressurized fuel from a high-pressure fuel supply pump; a detecting means for detecting an operating state of an engine; and an injector for injecting fuel supplied from said common rail into a combustion chamber, said injector divides fuel injection into the main injection and the pilot injection with an interval period prior to said main injection, in accordance with an operating state of the engine detected by the detecting means; a controller for calculating command pulses and outputting drive signals corresponding to said command pulses to the injector; wherein said controller calculates the interval period prior to said main injection, a pilot injection end delay period from the pulse end of said pilot injection command pulse to the pilot injection end, and a period corresponding to pulse width of said pilot injection command pulse corresponding to said pilot injection quantity, in response to said operating state of the engine as detected by said detecting means, and said controller sets the pulse start time of said pilot injection command pulse by being advanced by said interval period, said pilot injection end delay period and said period corresponding to pulse width of said pilot injection command pulse from previously determined injection start time of said main injection.
By adopting this composition, the controller calculates the pilot injection end delay period from the pulse end time of the pilot injection command pulse to the injection end time of the pilot injection, based on the operating state of the engine. This calculation derives the pilot injection end delay time, but it is also possible to read this out from a map, rather than performing function-based calculation. Consequently, the pilot injection end delay period is inferred accurately based on the operating state of the engine, and by taking this pilot injection end delay time into account when determining the pulse start time of the pilot injection command pulse, it is possible reliably to ensure the interval period which separates the pilot injection and the main injection, and to improve the controllability of the pilot injection, even when the common rail fuel pressure is high, thereby preventing deterioration of the pilot injection""s functions of suppressing noise, improving exhaust gas characteristics, and the like.
The controller calculates the pilot injection end delay period based on the fuel pressure in the common rail as detected by a pressure sensor provided in the common rail, or a target fuel pressure in the common rail calculated based on the operating state of the engine. Desirably, the common rail fuel pressure is the actual fuel pressure in the common rail as detected by a pressure sensor, but if the fuel pressure in the common rail has good controllability, then a target fuel pressure in the common rail may also be used. A target fuel pressure in the common rail may be derived from a map, or the like, based on the engine revolutions and accelerator operation amount, detected as the operating state of the engine.
Moreover, the controller sets the pilot injection end delay period to a greater value, as the fuel pressure in the common rail increases. By setting a longer pilot injection end delay period so as to advance the pulse start time of the pilot injection command pulse, as the common rail fuel pressure increases, it is possible to ensure the interval period between the pilot injection and the main injection by preventing delay to the end of the pilot injection even when the common rail fuel pressure is high.
Each of the injectors comprises: a pressure control chamber into which a portion of the fuel supplied from the common rail is introduced; a needle valve which opens and closes nozzles for injecting fuel formed in the front end section of the injector, by being raised or lowered based on the action of the pressure of fuel inside the pressure control chamber; an open/shut valve for releasing the fuel pressure inside the pressure control chamber by discharging fuel from inside the pressure control chamber; and an actuator for operating the open/shut valve.
Desirably, the common rail fuel injection device according to the present invention comprises: an engine revolution speed sensor for detecting engine revolution speed; an accelerator operation amount sensor for detecting the amount of operation of the accelerator; and a pressure sensor for detecting the fuel pressure in the common rail; and the controller calculates a total fuel injection quantity based on the engine revolution speed detected by the engine revolution speed sensor and the accelerator operation amount as detected by the accelerator operation amount sensor, determines the pilot injection quantity, the interval period and the main injection start time on the basis of the total fuel injection quantity and the engine revolution speed, determines an injector drive delay period from the pulse start time of the main injection command pulse to the injection start time of the main injection, based on the interval period and the common rail fuel pressure, and sets the pulse start time of the main injection command pulse by advancing the injector drive delay period with respect to the main injection start time.
Desirably, the controller determines the pulse width of the pilot injection command pulse based on the pilot injection quantity and the common rail fuel pressure.
Desirably, the controller calculates the main injection quantity by subtracting the pilot injection quantity from the total fuel injection quantity, determines a basic pulse width for the main injection command pulse based on the common rail fuel pressure and the main injection quantity, determines a correction pulse width for the main injection command pulse based on the common rail fuel pressure and the interval period, and calculates the pulse width of the main injection command pulse by summing the basic pulse width and the correction pulse width.
Desirably, the main injection start time, the interval period, the pilot injection end delay period, and the pulse width and pulse start time of the pilot injection command pulse are values expressed in crank angle units.
Desirably, the main injection start time and the pulse start time of the pilot injection command pulse is values with respect to the top dead centre.
Desirably, the common rail fuel injection device according to the present invention is applied to a diesel engine.
Moreover, the present invention also relates to a fuel injection control method for a common rail fuel injection device comprising: a common rail for accumulating pressurized fuel from a high-pressure fuel supply pump; a detecting means for detecting an operating state of an engine; and an injector for injecting fuel supplied from said common rail into a combustion chamber, said injector divides fuel injection into the main injection and the pilot injection with an interval period prior to said main injection, in accordance with an operating state of the engine detected by the detecting means; a controller for calculating command pulses and outputting drive signals corresponding to said command pulses to the injector; wherein said controller calculates the interval period prior to said main injection, a pilot injection end delay period from the pulse end of said pilot injection command pulse to the pilot injection end, and a period corresponding to pulse width of said pilot injection command pulse corresponding to said pilot injection quantity, in response to said operating state of the engine as detected by said detecting means, and said controller sets the pulse start time of said pilot injection command pulse by being advanced by said interval period, said pilot injection end delay period and said period corresponding to pulse width of said pilot injection command pulse from previously determined injection start time of said main injection.
Desirably, the controller calculates the pilot injection end delay period based on the fuel pressure in the common rail as detected by a pressure sensor provided in the common rail, or a target fuel pressure in the common rail calculated from the operating state of the engine.
Desirably, the controller sets the pilot injection end delay period to a greater value, as the fuel pressure in the common rail.
Desirably, the injectors each comprise: a pressure control chamber into which a portion of the fuel supplied from the common rail is introduced; a needle valve which opens and closes nozzles for injecting fuel formed in the front end section of the injector, by being raised or lowered due to the action of the pressure of fuel inside the pressure control chamber; an open/shut valve for releasing the fuel pressure inside the pressure control chamber by discharging fuel from inside the pressure control chamber; and an actuator for operating the open/shut valve.
Desirably, the common rail fuel injection device comprises: an engine revolution speed sensor for detecting engine revolution speed; an accelerator operation amount sensor for detecting the amount of operation of the accelerator; and a pressure sensor for detecting the fuel pressure in the common rail; and the controller calculates a total fuel injection quantity based on the engine revolution speed detected by the engine revolution speed sensor and the accelerator operation amount as detected by the accelerator operation amount sensor, determines the pilot injection quantity, the interval period and the main injection start time based on the total fuel injection quantity and the engine revolution speed, determines an injector drive delay period from the pulse start time of the main injection command pulse to the injection start time of the main injection, based on the interval period and the common rail fuel pressure, and sets the pulse start time of the main injection command pulse by advancing the injector drive delay period with respect to the main injection start time.
Desirably, the controller determines the pulse width of the pilot injection command pulse based on the pilot injection quantity and the common rail fuel pressure.
Desirably, the controller calculates the main injection quantity by subtracting the pilot injection quantity from the total fuel injection quantity, determines a basic pulse width for the main injection command pulse based on the common rail fuel pressure and the main injection quantity, determines a correction pulse width for the main injection command pulse based on the common rail fuel pressure and the interval period, and calculates the pulse width of the main injection command pulse by summing the basic pulse width and the correction pulse width.
Desirably, the main injection start time, the interval period, the pilot injection end delay period, and the pulse width and pulse start time of the pilot injection command pulse are values expressed in crank angle units.
Desirably, the main injection start time and the pulse start time of the pilot injection command pulse is values with respect to the top dead centre.
Desirably, the fuel injection control method for a common rail fuel injection device according to the present invention is applied to a diesel engine.